Exploring transmission Kikuchi diffraction using a Timepix detector

Electron backscatter diffraction (EBSD) is a well-established scanning electron microscope (SEM)-based technique [1]. It allows the non-destructive mapping of the crystal structure, texture, crystal phase and strain with a spatial resolution of tens of nanometers. Conventionally this is performed by placing an electron sensitive screen, typically consisting of a phosphor screen combined with a charge coupled device (CCD) camera, in front of a specimen, usually tilted 70° to the normal of the exciting electron beam. Recently, a number of authors have shown that a significant increase in spatial resolution is achievable when Kikuchi diffraction patterns are acquired in transmission geometry; that is when diffraction patterns are generated by electrons transmitted through an electron-transparent, usually thinned, specimen. The resolution of this technique, called transmission Kikuchi diffraction (TKD), has been demonstrated to be better than 10 nm [2,3]. We have recently demonstrated the advantages of a direct electron detector, Timepix [4,5], for the acquisition of standard EBSD patterns [5]. In this article we will discuss the advantages of Timepix to perform TKD and for acquiring spot diffraction patterns and more generally for acquiring scanning transmission electron microscopy micrographs in the SEM. Particularly relevant for TKD, is its very compact size, which allows much more flexibility in the positioning of the detector in the SEM chamber. We will furthermore show recent results using Timepix as a virtual forward scatter detector, and will illustrate the information derivable on producing images through processing of data acquired from different areas of the detector. We will show results from samples ranging from gold nanoparticles to nitride semiconductor nanorods

Niobium-based superconducting nano-devices fabrication using all-metal suspended masks

We report a novel method for the fabrication of superconducting nanodevices based on niobium. The well-known difficulties of lithographic patterning of high-quality niobium are overcome by replacing the usual organic resist mask by a metallic one. The quality of the fabrication procedure is demonstrated by the realization and characterization of long and narrow superconducting lines and niobium-gold-niobium proximity SQUIDs

Diffractive triangulation of radiative point sources

We describe a general method to determine the location of a point source of waves relative to a twodimensional single-crystalline active pixel detector. Based on the inherent structural sensitivity of crystalline sensor materials, characteristic detector diffraction patterns can be used to triangulate the location of a wave emitter. The principle described here can be applied to various types of waves, provided that the detector elements are suitably structured. As a prototypical practical application of the general detection principle, a digital hybrid pixel detector is used to localize a source of electrons for Kikuchi diffraction pattern measurements in the scanning electron microscope. This approach provides a promising alternative method to calibrate Kikuchi patterns for accurate measurements of microstructural crystal orientations, strains, and phase distributions

MACHe3, a prototype for non-baryonic dark matter search: KeV event detection and multicell correlation

Superfluid He3 at ultra-low temperatures (100 microKelvins) is a sensitive medium for the bolometric detection of particles. MACHe3 (MAtrix of Cells of Helium 3) is a project for non-baryonic dark matter search using He3 as a sensitive medium. Simulations made on a high granularity detector show a very good rejection to background signals. A multicell prototype including 3 bolometers has been developed to allow correlations between the cells for background event discrimination. One of the cells contains a low activity Co57 source providing conversion electrons of 7.3 and 13.6 keV to confirm the detection of low energy events. First results on the multicell prototype are presented. A detection threshold of 1 keV has been achieved. The detection of low energy conversion electrons coming from the Co57 source is highlighted as well as the cosmic muon spectrum measurement. The possibility to reject background events by using the correlation among the cells is demonstrated from the simultaneous detection of muons in different cells

Studie: Verteilte Publikationserstellung mit Microsoft Word und den Microsoft SharePoint Services

Der Prozess des wissenschaftlichen Publizierens stellt besondere Anforderungen an die eingesetzte Standardsoftware. Verschiedene Autoren arbeiten gemeinsam an Dokumenten, was aufgrund mangelnder Koordination und informationstechnischer Unterstützung in der Regel zur uneinheitlichen Verwendung von Begrifflichkeiten und Schreibweisen führt. Passagen einzelner Autoren müssen in getrennten Dokumenten verfasst und bei der Zusammenführung abgeglichen werden. Dokument- und Formatvorlagen helfen bei der Einhaltung der Konsistenz im Layout, jedoch ist auch hier in der Regel eine Anpassung notwendig. Literatur-, Stichwort- und Abbildungsverwaltung lassen sich derzeit nur mit einem Konglomerat an Software (z. B. Textverarbeitungsprogramm in Kombination mit Literaturverwaltungssoftware und Literaturrecherchediensten) - zumeist nur unzureichend und auf Einzelbenutzerebene - lösen. Eine Abstimmung zwischen den Autoren während des ganzen Publikationsprozesses wird lediglich durch E-Mail und Korrekturfunktionalitäten im Publikationsprozess unterstützt. Einblicke in den Arbeitsfortschritt anderer Autoren sind kaum möglich. Die aufgeführten Probleme verstärken sich bei zunehmender Autorenzahl und steigender räumlicher und zeitlicher Distanz zwischen den Autoren, die zukünftig durch zunehmende Forschung auf europäischer und internationaler Ebene noch steigen wird. Ziel dieser Studie ist die Evaluation der Unterstützung für das verteilte, wissenschaftliche Publizieren durch Microsoft Word 2003 in Verbindung mit den Microsoft SharePoint Services 2003. Verteiltes, wissenschaftliches Publizieren wird hier als die verteilte Erstellung von wissenschaftlichen Publikationen verstanden. Im Rahmen der Studie wird daher Microsoft Word alleine mit der Word-SharePoint-Services-Kombination (Word und SharePoint Services) und den Konkurrenzprodukten OpenOffice.org und (La)TeX verglichen. Im Rahmen des Vergleichs werden insbesondere Verbesserungen hervorgehoben und quantifiziert, die sich aus der Verwendung der Microsoft SharePoint Services für die Anforderungen des wissenschaftlichen Publizierens ergeben. Weiterhin bestehende Defizite für dieses Aufgabenumfeld werden expliziert und bewertet. Die Ergebnisse werden im Anschluss an die Evaluation als Grundlage zur fachkonzeptuellen Spezifikation einer Publikationsarchitektur zur integrierten Unterstützung des wissenschaftlichen Publikationsprozesses auf Basis von Microsoft-Produkten dienen. Zur validierten Erhebung der Anforderungen wird zunächst der Prozess des wissenschaftlichen Publizierens erfasst und dokumentiert. Anforderungen, die sich sowohl aus dem Publikationsprozess als auch an die Publikation ergeben, werden zusammengetragen und mithilfe einer Mind Map visualisiert und strukturiert. Im Anschluss wird ein Erfahrungsbericht zur Nutzung der Word-SharePoint-Services-Kombination im Rahmen einer Konferenzveröffentlichung gegeben

Modeling Antarctic tides in response to ice shelf thinning and retreat

Tides play an important role in ice sheet dynamics by modulating ice stream velocity, fracturing, and moving ice shelves and mixing water beneath them. Any changes in ice shelf extent or thickness will alter the tidal dynamics through modification of water column thickness and coastal topography but these will in turn feed back onto the overall ice shelf stability. Here, we show that removal or reduction in extent and/or thickness of the Ross and Ronne-Filchner ice shelves would have a significant impact on the tides around Antarctica. The Ronne-Filchner appears particularly vulnerable, with an increase in M2 amplitude of over 0.5 m beneath much of the ice shelf potentially leading to tidally induced feedbacks on ice shelf/sheet dynamics. These results highlight the importance of understanding tidal feedbacks on ice shelves/streams due to their influence on ice sheet dynamics

Spontaneous Oscillations of Collective Molecular Motors

We analyze a simple stochastic model to describe motor molecules which cooperate in large groups and present a physical mechanism which can lead to oscillatory motion if the motors are elastically coupled to their environment. Beyond a critical fuel concentration, the non-moving state of the system becomes unstable with respect to a mode with angular frequency omega. We present a perturbative description of the system near the instability and demonstrate that oscillation frequencies are determined by the typical timescales of the motors.Comment: 11 pages, Revtex, 4 pages Figure

Affine modifications and affine hypersurfaces with a very transitive automorphism group

We study a kind of modification of an affine domain which produces another affine domain. First appeared in passing in the basic paper of O. Zariski (1942), it was further considered by E.D. Davis (1967). The first named author applied its geometric counterpart to construct contractible smooth affine varieties non-isomorphic to Euclidean spaces. Here we provide certain conditions which guarantee preservation of the topology under a modification. As an application, we show that the group of biregular automorphisms of the affine hypersurface $X \subset C^{k+2}$ given by the equation $uv=p(x_1,...,x_k)$ where $p \in C[x_1,...,x_k],$ acts $m-$transitively on the smooth part reg$X$ of $X$ for any $m \in N.$ We present examples of such hypersurfaces diffeomorphic to Euclidean spaces.Comment: 39 Pages, LaTeX; a revised version with minor changes and correction